In practice, various valve actuating drives are known and in use. Besides widely employed electrical valve actuating drives, these also include in particular fluid-operated valve actuating drives (see, for example, EP 0665381 B1, EP 1418343 B1, EP 1593893 B1 and EP 2101061 A1). Typically such fluid-operated valve actuating drives comprise a linear actuator, whose slide is coupled directly or indirectly with the input of the valve, and a base unit provided with the fluidic control system. This latter typically comprises an electrofluidic signal transducer, which in particular is disposed upstream from the fluidic control system and is able to cooperate therewith and may have a proportional output response. Furthermore, at a signal input in communication with the electrofluidic signal transducer or associated therewith, there is typically connected an external electrical regulating unit, which may comprise input means, a setpoint input, a regulating electronic unit, a communications unit, a signal output and/or a signal generator. In the sense of a closed regulating circuit, the actual-value signal of a measuring sensor associated with the valve may then be fed back to the electrical regulating unit.
EP 884481 A2 discloses a pneumatic position regulator for a pneumatic actuating drive, whose manipulated variable is corrected to an adjustable setpoint value, especially for positioning of membrane-actuated and piston-actuated regulating valves in proportion to a pneumatic input signal. In order to avoid pressure losses, this position regulator is equipped with three main components, namely a comparator, which compares the manipulated variable with the setpoint value and outputs a difference value, a first valve, which is disposed in the flow path from a pneumatic pressure source to the actuating drive, is closed in the rest condition and can be activated by the difference value, and a second valve, which is disposed in the flow path from a relief aperture of the actuating drive to a pressure sink, is closed in the rest condition and can be activated by the difference value. The regulating circuit of the position regulator contains a pneumatic actuating drive with a positioning element in the form of an actuating rod, which couples the manipulated variable to the element determining the flow through the valve, slide or the like. The actuating drive is provided with a pressure-urged membrane, with which the positioning element is connected. The stroke movement of the positioning element is output via a mechanism, preferably a cam mechanism with exchangeable cam disks, to the one end of a compression spring, whose other end loads the one arm of a double-armed lever, which is mounted pivotally at its center. A pressure/force transducer containing a membrane urged by a setpoint pressure presses on the same lever arm as the compression spring, but in opposite direction. The force exerted by the compression spring on the lever arm is compared in the capture range of the regulating circuit with the opposing force exerted via the membrane, by the fact that an equilibrium is established between these forces. Together with the compression spring, the pressure/force transducer therefore forms a setpoint/actual value comparator. In this comparator, the compression spring together with the cam mechanism disposed upstream from it forms a displacement/force transducer, which converts the stroke of the positioning element into the actual-value force.
DE 3819122 C2 discloses a method for regulating the position of servo valves with fluid or with regulated actuating drives operated by electric motors, wherein the deviations between the actual and the ideal correlation of reference variable and controlled variable of the servo valve is sensed as a function of the direction of movement in a preliminary test and a correction value formed from this deviation is delivered to the comparator of reference variable and controlled variable on the regulating device. The delivery of the correction value takes place in the form of a change of the signals of reference and/or controlled variable delivered to the comparator. This correction value is delivered to the regulating device in such a way that the deviation of the correlation of reference variable and controlled variable caused by the hysteresis of the system comprising servo valve with regulated actuating drive is compensated.